For production of an L-amino acid by fermentation, a strain isolated from the natural world or an artificial mutant of the strain has been used to improve productivity. For example, in the case of L-lysine, many artificial mutants producing L-lysine are known, and most of them are mutants resistant to S-2-aminoethylcysteine (AEC) and belong to the genus Brevibacterium, Corynebacterium, Bacillus or Escherichia. Also, there have been proposed various technics for increasing amino acid production such as use of a transformant obtained by using a recombinant DNA (U.S. Pat. No. 4,278,765).
The technics are mostly based on enhancement of an activity of an enzyme involved in an amino acid biosynthetic pathway, conversion of the enzyme to that desensitized in inhibition and the like (As to bacterium belonging the genus Escherichia, see Japanese Patent Application Laid-Open No. 56-18596 (1981) and International Publication No. WO 95/16042).
On the other hand, as an example of improvement of amino acid productivity by enhancing an amino acid excretion protein, a bacterium belonging to the genus Corynebacterium in which an L-lysine excretion gene, lysE is enhanced is known. However, as to bacteria belonging to the genus Escherichia, it is unknown even whether an L-amino acid excretion protein is present or not. Therefore, it is unknown whether enhancement of the L-amino acid excretion protein is effective in L-amino acid production using a bacterium belonging to the genus Escherichia or not.
Although the entire nucleotide sequence of E. coli strain K-12 belonging to the genus Escherichia has been already determined (Science, 277, 1453-1474(1997)), there are a large number of proteins of which functions are unknown.